Initialize the MPI execution environment


#include "mpi.h"
int MPI_Init(argc,argv)
int  *argc;
char ***argv;

Input Parameters

Pointer to the number of arguments
Pointer to the argument vector

Command line arguments

MPI specifies no command-line arguments but does allow an MPIimplementation to make use of them.

print out the state of the message queues when MPI_FINALIZE is called. All processors print; the output may be hard to decipher. This is intended as a debugging aid.

print out the version of the implementation (not of MPI), including the arguments that were used with configure.

-mpinice nn
Increments the nice value by nn (lowering the priority of the program by nn). nn must be positive (except for root). Not all systems support this argument; those that do not will ignore it.

Start a debugger in an xterm window if there is an error (either detected by MPI or a normally fatal signal). This works only if MPICH was configured with -mpedbg.

If MPICH was built with -DMPIR_DEBUG_MEM, this checks all malloc and free operations (internal to MPICH) for signs of injury to the memory allocation areas.

-mpidb options
Activate various debugging options. Some require that MPICH have been built with special options. These are intended for debugging MPICH, not for debugging user programs. The available options include:
        mem     - Enable dynamic memory tracing of internal MPI objects
	memall  - Generate output of all memory allocation/deallocation
        ptr     - Enable tracing of internal MPI pointer conversions
	rank n  - Limit subsequent -mpidb options to on the process with
	          the specified rank in MPI_COMM_WORLD.  A rank of -1
		  selects all of MPI_COMM_WORLD.
        ref     - Trace use of internal MPI objects
        reffile filename - Trace use of internal MPI objects with output
	          to the indicated file
	trace   - Trace routine calls


Note that the Fortran binding for this routine has only the error returnargument (MPI_INIT(ierror))

Because the Fortran and C versions of MPI_Init are different, there isa restriction on who can call MPI_Init. The version (Fortran or C) mustmatch the main program. That is, if the main program is in C, thenthe C version of MPI_Init must be called. If the main program is inFortran, the Fortran version must be called.

On exit from this routine, all processes will have a copy of the argumentlist. This is not required by the MPI standard, and truely portable codesshould not rely on it. This is provided as a service by thisimplementation (an MPI implementation is allowed to distribute thecommand line arguments but is not required to).

Command line arguments are not provided to Fortran programs. Moreprecisely, non-standard Fortran routines such as getarg and iargchave undefined behavior in MPI and in this implementation.

The MPI standard does not say what a program can do before an MPI_INIT orafter an MPI_FINALIZE. In the MPICH implementation, you should doas little as possible. In particular, avoid anything that changes theexternal state of the program, such as opening files, reading standardinput or writing to standard output.

Signals used

The MPI standard requires that all signals used be documented. The MPICHimplementation itself uses no signals, but some of the software that MPICHrelies on may use some signals. The list below is partial and shouldbe independantly checked if you (and any package that you use) dependon particular signals.



-mpedbg switch


Meiko CS2


ch_p4 device


Intel Paragon (ch_nx and nx device)


Shared Memory (ch_shmem device)


Note that if you are using software that needs the same signals, you mayfind that there is no way to use that software with the MPI implementation. The signals that cause the most trouble for applications includeSIGIO, SIGALRM, and SIGPIPE. For example, using SIGIO andSIGPIPE may prevent X11 routines from working.


All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the lastargument. Before the value is returned, the current MPI error handler iscalled. By default, this error handler aborts the MPI job. The error handlermay be changed with MPI_Errhandler_set; the predefined error handlerMPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue pastan error.

No error; MPI routine completed successfully.
This error class is associated with an error code that indicates that an attempt was made to call MPI_INIT a second time. MPI_INIT may only be called once in a program.